accurate measurement of pipe loss
The saying “What you don’t know can’t hurt you” obviously was not created for the underground pipeline asset management industry. In fact, what you don’t know underground can potentially cause catastrophic failures and financial woes that may take years and millions of dollars to recover from.
Recent advancements in inspection technologies now allow for improved and comprehensive analysis complementing existing CCTV inspections to better cover assets. In the simplest terms, pipe or material loss equals income loss. Read below to find out more on how to better understand the existing condition of the infrastructure using the latest advancements in LADAR technology. With LADAR, you can get measurable data, allowing for better maintenance and rehabilitation decisions.
Pipe loss in wastewater pipes can be caused by hydraulic, mechanical, or chemical action on exposed pipe surfaces. For example, fast moving water or cleaning operations can create deep gouges, grooves and channels in otherwise healthy pipe. Similarly, hydrogen sulfide gas is infamous for its ability to relentlessly corrode concrete pipes. Regardless of the source, an essential element of a comprehensive pipe inspection program is to be able to detect, accurately measure, and monitor pipe loss rates over time.
Pipe loss is often detected during standard CCTV inspections. During these inspections, visual cues of pipe loss are recognized by the camera operator and associated with a specific cause. For example, surface spalling and exposed rebar may be associated with chemical corrosion caused by the sustained presence of hydrogen sulfide gas. Similarly, gouges or channels near the inlet of fast moving water might be attributed to persistent hydraulic action. While CCTV inspections excel at detecting pipe loss, they provide only a qualitative means measuring pipe loss. Often, these subjective estimates are incorrect.
A comprehensive pipe inspection program should supplement traditional CCTV inspections with sensors capable of accurately measuring lost material. Pipe loss can be accurately measured using Laser Detection and Ranging (LADAR). The most prevalent approach used in the industry uses an approach called structured light to provide a cross-sectional analysis of pipe geometry. In this 2-D approach, the CCTV camera is augmented with a ring, or circular, laser to provide cross-sectional measurements by measuring the deflection of the ring laser in the camera. These measurements can be used to measure pipe loss as well as provide other useful information such as pipe ovality. While an improvement over CCTV, Two-dimensional profiling approaches are inaccurate if the inspection sensors are not properly aligned within the pipe. For example, in a 64” pipe, a platform yaw of 10 degrees induces over 1” error into cross section measurements of horizontal diameter. This intolerance to sensor alignment errors can result in over-reporting of material loss and pipe deflection, resulting in unnecessary maintenance and rehabilitation spending.
Fortunately, a new class of inspection techniques are available that eliminate alignment errors and produces accurate pipe loss and cross sectional measurements. These techniques employ 3-D LADAR sensors that image an entire segment (as apposed to a single cross section) of the pipe to be inspected. Techniques from three-dimensional computer vision are used to correct for sensor alignment and compute accurate cross sections for pipes of any shapes. Furthermore, these sensors do not employ CCTV cameras as do the 2-D structured light systems; consequently, they can operate in complete darkness and work just as well in small and large pipe systems.
